Miniaturization of semiconductor devices has been advanced in recent years and the process margin in device manufacture has been narrowed very much. In such a situation, it is important to manage the size of miniaturized patterns as a way of process management for eliminating failure of products and improving yield.
Here, in FIGS. 13 and 14, examples of currently used processes to which a pattern measurement is used in a semiconductor device manufacture are illustrated. FIGS. 13 and 14 are diagrams each illustrating an example of a process in a conventional semiconductor device manufacture in which a pattern measurement is used.
First, an oxide film and/or a metal film are formed on a semiconductor wafer in a process of deposition 20. Then, in a thickness measurement 21, a measurement is performed to check whether thicknesses of the formed films are uniform and satisfying a value of standard. When the measurement is cleared, a photosensitive resin film is applied in a resist application process in a lithography 22 as a next process, and then light is irradiated onto the semiconductor wafer through a mask in an exposure process.
Thereafter, in a development process, a part irradiated with the light is melted by a development solution when using a positive resist, and the part irradiated with the light remains when using a negative resist, thereby forming a resist pattern. When the process of the lithography 22 is finished, in an in-line measurement 23, a measurement of a size of the object pattern by CD-SEM (critical dimension scanning electron microscope), and a measurement of a shape of the object pattern by scatterometry are performed.
Thereafter, in an etching 24, a pattern is formed to the oxide film or metal film, and an in-line measurement 25 is performed in the same manner as the in-line measurement 23. Note that the “in-line measurement” is a measurement process embedded as one process in a device manufacture process, more specifically, it is a measurement process returns the wafer to the line again after the measurement.
In addition, as illustrated in FIG. 14, a result of the in-line measurement 23 is fed back to the lithography 22 and fed forward to the etching 24, and a result of the in-line measurement 25 is fed back to a manufacture apparatus of the etching 24, thereby performing process control for maintaining the pattern size.
Further, an example of a measurement object pattern is illustrated in FIGS. 15A and 15B. FIGS. 15A and 15B are diagrams illustrating schematic cross-sectional views of a wafer and a process flow in a conventional contact-hole forming process.
The wafer has a multi-layered configuration of a silicon (Si) substrate 40, a silicon oxide (SiO2) film 41 (wiring interlayer film), and a photoresist 42. A photoresist pattern formation is performed in FIG. 15A, and a pattern formation to the SiO2 film 41 by dry etching is performed in FIG. 15B so that a contact hole 43 is formed. Since a connection portion between a diffusion layer and a metal wiring layer such as the contact hole 43 has a small margin in the device manufacture, measurement and management of a size of the bottom of the hole is particularly expected to bring a yield improving effect by early discovery of failure.
As a measurement method of a miniaturized pattern, currently, CD-SEM is in the mainstream. A principle of CD-SEM is such that primary electrons emitted from an electron gun are irradiated onto a measurement sample, then secondary electrons evacuated from the sample are captured by a detector, and a size of the object pattern is measured from obtained intensity distribution of the secondary electrons.
In addition, an optical pattern shape measurement apparatus capable of obtaining three-dimensional shape information, for example, line width, height, sidewall angle, called scatterometry has been introduced in recent years.
Here, a measurement principle of the scatterometry is illustrated in FIG. 16.
First, in a step 51, a measurement model is created from information such as property values (refractive index, absorption coefficient), shape, and/or base film thickness, and, in a step 52, a calculated waveform is calculated from the created measurement model.
Next, in a step 53, a simulation is performed with sequentially changing shape parameters and a library is created from a plurality of calculated waveforms obtained.
Then, in a step 54, spectral waveforms are obtained by an optical system in the scatterometry apparatus. In a step 55, a detected waveform is obtained, and then, in a step 56, the calculated waveforms in the library created in the step 53 and the detected waveform obtained in the step 55 are compared. In a step 57, a calculated waveform having the highest degree of coincidence to the detected waveform is selected as a best-match calculated waveform.
In a step 58, line widths d1 and d2, a pattern height h1, film thicknesses h2 and h3, and a sidewall angle θ of the object pattern are calculated from the selected best-match calculated waveform.
A major reason for generally using the CD-SEM measurement and the scatterometry measurement as mentioned above is that both of them can be used in an in-line measurement. Merits of the CD-SEM measurement and the scatterometry measurement are such that an early cause investigation can be made when any abnormality is detected in the measurement in the CD-SEM because the CD-SEM can directly observe product patterns, and the object pattern can be measured at a high throughput in the scatterometry because it uses light in the measurement and thus the measurement is implemented in the air pressure different from the CD-SEM.
However, a demerit of the CD-SEM measurement and the scatterometry measurement is that only plane information can be obtained when a contact hole is measured by CD-SEM as illustrated in FIG. 17, and thus it is difficult to obtain three-dimensional shape information. FIG. 17 is a diagram illustrating an example of a conventional measurement on a contact hole by CD-SEM.
In the scatterometry, a dedicated TEG (test element group: characteristics evaluation element) for the scatterometry measurement should be used as a test pattern at a scribing part of a product wafer, and thus there is a problem that, when an abnormality exists in the product pattern, the abnormality cannot be directly observed.
As a countermeasure of such problems, a method of obtaining three-dimensional shape information of the product pattern using a scatterometry measurement result based on the CD-SEM measurement is described in Japanese Patent Application Laid-Open Publication No. 2004-219343 (Patent Document 1).
In addition, to improve throughput, calculated waveforms are calculated by simulations with previously changing hundreds of thousands to millions of measurement parameters from a calculation model, and a library as illustrated in FIG. 18 is created in the scatterometry. Therefore, there is a problem of large preparation load until the scatterometry is used in the in-line measurement.
FIG. 18 is a diagram illustrating a library of calculated waveforms obtained by simulations from a conventional calculation model.
As a countermeasure to such a problem, Japanese Patent Application Laid-Open Publication (Translation of PCT Application) No. 2008-530519 (Patent Document 2) describes a method of introducing s simpler calculation of the simulation by previously creating a model of only a film, and estimating a prediction value from the film model, and using the value.